1. Field of the Invention
This invention relates to a substantially phosphate-free dishwasher detergent containing at least an anhydrous alkali carbonate and an alkali metasilicate, in which at least two different cations must be present. The detergent is particularly adapted to being automatically dispensed in the dishwasher.
2. Statement of Related Art
To improve the ease of operation of modern dishwashing machines, particularly of the commercial or heavy-duty type, automatic detergent dispensing is a prime requirement. First, this means that the user does not come into contact unnecessarily often with alkaline detergent powders containing irritating chemicals and, second, this provides for a uniform metering and dispersion of detergent which in turn guarantees satisfactory cleaning of the soiled crockery. Automatic detergent dispensing is generally state-of-the-art and found on almost all dishwashers.
Powdered dishwasher detergents are automatically dispensed by means of conductivity meters which usually are coupled with overflow or flush-out dispensing units. In order to ensure complete and satisfactory dispensing of the powder from the dispensing system, the powder in the dispensers must not form lumps and/or harden when water flows in, and instead should form a stable, loose suspension.
Pending use, detergents are generally stored and, accordingly, are required to show favorable storage behavior even at elevated temperatures, which occasionally may rise to around 50.degree. C., i.e. they must never cake or harden but should retain the flowability with which they were produced. These properties are essential for loading and stocking the above mentioned automatic dispensers.
Previously, it has been possible to produce storable and dispensable dishwashing detergents having the above properties by using suitable commercially available raw materials, particularly specially prehydrated sodium tripolyphosphates. This standard, however, could not readily be maintained for phosphate-free detergents. Tests were conducted with powdered detergents containing: anhydrous sodium carbonate; sodium metasilicate. 5H.sub.2 O and sodium hydroxide or sodium carbonate. 10H.sub.2 O; anhydrous metasilicate and anhydrous sodium sulfate or sodium carbonate. 10H.sub.2 O; anhydrous sodium metasilicate and Na citrate. 2H.sub.2 O or anhydrous sodium carbonate; sodium metasilicate. 5H.sub.2 O and anhydrous dichloroisocyanurate or dichloroisocyanurate containing water of hydration or borax. 10H.sub.2 O; and anhydrous sodium metasilicate. Some tests resulted in very rapid hardening of the mixtures in the dispenser, so that the detergent could not be properly flushed out of the dispenser into the dishwashing machine, thus ruling out any possibility of automatic dispensability. Alternatively, the detergents were not stable in storage because in standard commercial packs, such as bags and drums, they hardened after only a few days at an elevated temperature such as 40.degree. C., and could no longer be dispersed. No foreign agents for this application could be found.